Brushes having thermoplastic bodies and bristles are known. Such brushes can be manufactured by injection molding.
In many manufacturing processes, the thermoplastic bodies and bristles are "welded" to one another. One of the problems in these processes is to establish a durable connection between the body of a brush and the bristles. The European Patent Specification 0 142 885 discloses a procedure in which the bristles of a tuft are melted at one end in order to bond the individual bristles to each other and to form an enlargement. When the body of the brush is injection molded around the enlargement, the bristles are locked to the body.
The mold used for injection molding has passages which accommodate the bristles during the molding operation. Due to the high pressures employed for injection molding, another problem arises during the molding operation, namely, that of sealing the passages so that the injection molded material cannot enter the passages. The sealing problem is made more difficult by the fact that the cross-sectional areas of the tufts may not all be the same because the number of bristles per tuft can vary. Many procedures for sealing the passages are known. For instance, the German patent 29 22 877 provides the ends of the passages adjacent the brush body with constrictions or makes these ends conical.